In electro-dip lacquering, also termed electrophoretic lacquering, the lacquer components in the lacquer bath are deposited on the workpieces under the influence of an electric field. It has proved advisable not to keep the electric field constant during the passage of the workpieces through the lacquer bath, but to vary it along the movement path, in particular to let it increase with the distance covered. A reason for this measure inter alia is that the lacquer coating building up represents an electrical resistance, which makes the further build-up of the lacquer coating difficult.
The problem thus arises of how the voltage can be changed for each workpiece as it passes through the lacquer bath. In electro-dip lacquering devices of the type named at the beginning, such as described for example in DE 199 42 556 C2, the current is supplied to the workpiece via a contact rail divided into individual sections in the movement direction of the workpieces to be lacquered; the sections are galvanically separated and connected to one pole of a voltage source assigned to each section. The electrodes arranged along the movement path of the workpieces in the lacquer bath are connected to the other pole of the voltage source. It is disadvantageous in this case that it is relatively difficult to track the path of each individual workpiece along the various sections of the contact rail in control terms and to effect the transition of the workpiece from one section to another section without “jump” in potential. Since the charge flowing between electrode and workpiece is used as a measure for the coating thickness applied, it is necessary to “activate” the measurement of the current flowing to the workpiece section-wise too with the movement of the workpiece. After all, the “cuts” in the contact rails which cause the galvanic separation also represent unevennesses in the contact rail which lead to wear of the contact devices that are moved together with the workpieces.
In the event of changes in the workpiece, e.g. in the length of the workpiece, or in the event of a change in the dipping curve, the positions of the cuts between the contact rail sections change, so that an installation change is necessary for an optimum coating.
The present invention is directed to resolving these and other matters.